Conversion of hydrocarbon gases



pril 30, 1940.

R. F. MARscHNER CONVERSION OF HYDRQCARBON GASES Filed Jan. 6, 1938 Rober/E Marsa/:ner

lNvENToR ATTORNEY suitablefor motor fuel andhaving high anti-l gases.

Patented Apr. 30, 1940 PATENT v ofi-Fics v awaits l l CONVERSION oF nYDRocAaBoN casas Robert F. Marschner, Chicago, Ill., ril-signor to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application January s, 193s, semina. laatst y 11 Claims. This invention relates to conversion of mixtures of butanes and butylenes into motor fuel and particularly their conversion into octanes knock characteristics. In the manufacture of motor fuels from crude petroleum, natural gases and cracking still products, the gasoline fraction commonly contains dissolved therein lower boiling hydrocarbons which are normally gaseous and which tend to increase the vapor pressure of the gasoline to an undesirable extent. It is common practice, therefore, vto separate the normally gaseous hydrocarbons from the gasoline, particularly the propane whichshould be completely removed in order toreduce the Reid vapor pressure of the gasoline as much as possible. It is common practice to allow-a certain amount of the butanes and butylenes to remain in the gasoline but the amount of butanes and butylenes occurring in casinghead 4gasoline -and cracking still products in particular is ordinarily too great to permit allowing all of them to remain in thel gasoline without excessively increasing the Reid vapor pressure which results in gasoline losses by evaporation.

It is the purpose of this invention tomore economically utilize the excess butanes and butylenes and particularly the butane-butylene mixturesl obtained from cracking processes, either directly from the stabilization of the cracked gasoline or indirectly by absorption from the cracking still The butanes and butylenes thus obtained comprise a mixture of isobutylene, isobutane, normal butane and the two isomeric normal butylenes designated 1 and 2. Hereinafter mixtures' of these various hydrocarbonsof four carbon atoms will be referred to as C4 hydrocarbons. The ,C4 hydrocarbons obtained from cracking still products will usually contain about 10l5% of isobutylene, 2030% of normal butylenes, the remainder being iso-butane and'normal butane.

- The amount of normal butane will usually exceed natural gases is substantially devoid of butylenes and when used in my process will be hantilec'lA considerably the amount of iso-butane. The C4 hydrocarbon fraction obtained from crude oil distillation and from casinghead gasoline and somewhat differently for this reason.

In order to convert the C4 hydrocarbons to octanes it is rst necessary to effect a polymerization, or condensation lof two molecules of the C4 hydrocarbons and various methods have been proposed vfor accomplishing this result. One method consists of subjecting the butane or butane-butylene mixture to pyrolysis at high tem- (Ctisc-lo) yperature with theresult that the-butane is extensively decomposed with concurrent interacfullers earth or phosphoric acid. 'Theoctene' may be later hydrogenated tolproduce octane. The purpose of my invention is to effect certain improvements in the ylatter process.- by which higher yields of octane may be obtained and particularly those octane isomers maybe obtained which possess the higher, more desirable anti- 'knock characteristics. The invention may be readily understood by referring to the accompanying. drawing which'formsa part of Athis specification and which show's atically the various steps of the process;-

Referring to the drawing, C4 hydrocarbons arev introduced by line Iii leading to heater il where` the temperature is raised to about Z50-350 F. .The heated hydrocarbons are conducted by transfer line l2 under pressure'of -aboutilvto 200 pounds per sq. in. to catalyst chamber t3V where the heated butanes are intimately contacted with a bed of catalytic material. On contact with the catalyst the butylenes, and especially the isobutylene in the hydrocarbon stream, n are polymerized to produce iso-octenes and some of the butylenes also react with the butans to produce octanes. duced in this manner are branched chain compounds and are ordinarily called iso-octenes and iso-octanes respectively. They are especially valuable for motorv fuels because of their high antiknock characteristics. The normal octane, on the other hand, is quite undesirable as a motor fuel becauseY of its pronounced tendency toward detonation. Higher pressures may-be employed in the polymerizer I3, for example 1000 lbs., in

vWhich'case the reacting mass will be largely in the The octenes and octanes prosures are usually desirable. After passing through the catalyst' in chamber I 3 the butanes are conducted by line I4 to heat exchanger I5 and condenser I5 wherein the polymerized products are condensed and separated as a liquid layer iri separator I1. This liquid, consisting mostly ofV octenes, is withdrawn by line I8 and pump I9 which forces it into fractionator where unchanged C4 hydrocarbons are removed as a vapor by line 2|. Octenes are withdrawn by line 22 and forced by pump 23 into heater 24 where the temperature ls increased to about 500-700 F.V Hydrogen introduced by line 25 is simultaneously heated with the octenes and the mixture is conducted by line 26 at a pressure of 500 to 3000 lbs. per sq. in. to the hydrogenation Ychamber 21, suitably charged with a hydrogenation catalyst which may be molybdenum suliide, zinc chromate, etc. or, if desired, hydrogenation may be conducted at lower pressures, and temperatures by employing the metal type catalysts such as nickel, platinum, etc. Pressures used with the metallic catalysts of the nickel type or refractory oxide catalysts of the copper chromite type may be in--the range of atmospheric to 200 lbs., in which case pump 23 may be dispensed with. Nickel or copper chromite may be employed at a temperature of about 500 F.

'The octenes are converted by hydrogenation in 21 to octanes which are withdrawn by line 28 and condensed in condenser 29, from which they-are discharged to receiver 30, from which excess hydrogen may be separated by line 3l and the final product Withdrawn by line 32.

'Ihe uncondensed gases 1n separator I1, consisting principally of butanes with some n-butylenes, are withdrawn by line 33 leading to heat exchanger I5 where they are heated and thence-by line 33a to furnace 34 where the temperature is further raised to about '850-1000 F. 'Ihe pressure is reduced in line 33a by pressure reducing valve 36 to approximately atmospheric or slightly higher, e. g., v pounds per sq. in. The gases are introduced by line 35 into dehydrogenating .a chamber 31 where they contact a suitable dehydrdgenating catalyst, which may be the same catalysts as were employed in hydrogenator 21, with the exception of platinum, but due to the higher temperature and lower pressureV in dehydrogenator 31 and the necessity for occasional regeneration, these catalysts may be prepared or pretreated in a different way. The temperature of dehydrogenation chamber 31 may be 850-1000" F. The mixture of gases is withdrawn by line38, cooled by heat exchanger and cooler 39 and then forced by compressor 40 into fractionato'r 4I where hydrogen is separated from the butylenes produced by the dehydrogenatiorn Cooling coil 42 serves to condense out hydrocarbons from the hydrogen gas which is then conducted by line 43 tocompressor 44 and byline 25 to heater 24 previously described. 'I'he pressure to which the hydrogen is compressed by compressor 44 will depend upon the pressure re- Aquired for the hydrogenation operation in chamber 21. Where nickel or other metallic catalyst or copper chromite is employed therein it is not necessary to employ high pressures and, in fact, the hydrogenation may be conducted at approximately atmospheric pressure, although it is usually desirable to employ somewhat higher pressures, e. g., 100-500 lbs. per sq. inch. Where sulfactive catalysts of the type of molybdenum sulde and certain chromates are employed, much higher pressures are necessary, e. g., about 2,000

pounds per sq. inch. In this case it will be necessary to operate compressor 44 whereas in the case where nickelcatalysts are used compressor 44 may be bypassed. It may be necessary when employing nickel catalysts, to regulate vthe sulfur content of the polymer, preferably by introducing a scrubber in line I0.

Returning to fractionator 4I, any high boiling constituents of the stream withdrawn from dehydrogenator 31 may be discarded by line 45. "Butanes containing about 30-50% of butylenes are withdrawn as a side stream by line 46 and pump 41 and thence by line 48 to heater I I previously described where the butylenes are combined with the mixed C4 hydrocarbons, heated in heater Il and polymerized in chamber I3, increasing the yield of the desired butylene polymers obtained in this operation. In order to produce a polymer of higher antiknock value, however, I prefer to isomerize the butylenes to convert some of the l-butene to 2butene and isobutylene before polymerization. The butylenes in the stream flowing through line 48, contain a deficiency of isobutylene. I prefer to increase the concentration of normal 2butene and isobutylene before introducing it into heater II and polymerizer I3 and this I may accomplish in the following manner. Valve 49 may be closed. Valves 50 and 5I may be opened to divert the stream of butylenes through heater 52 and catalyst vchamber 53. Chamber 53 may be packed 'with a porous-catalyst consisting of aluminum .II may be bypassed and the hot vapors from 53 may be conducted directly by line 55 to polymerizer I3 where the 2butene and isobutylene are converted to octene of high knock rating.

By operating catalyst chamber 53 at a higher temperature, for example 480-620" F., preferably about 575 F., and employing a contact time of about 2 to lminutes, for example 5 minutes, I may obtain a larger conversion of normal butylene into isobutylene, the amount of conversion depending on the contact time, temperature and 'the catalyst employed. Thus I may convert about 10 to 40% of the butylene to iso-butylene, the remainder being largely converted from 1-butene to 2butene.' In one run-over H3PO4- kieselguhr catalyst at 570 F. and 250 sec. contact time, l-butene gave a gaseous product in which 50% of the olen content was isobutylene.

Some polymerization of butylenes to octenes and even higher boiling compounds' occurs simultaneously Withthe isomerization to isobutylene'and I thereforeprefer to introduce the product from this reaction by lines 54 and 55 directly to the polymerizer and recover the polymers produced in chamber 53 along with the polymers obtained in chamber I3.

In order to reduce the extent of undesirable polymerization occurring in chamber. 53 I may dilute 'the C4 hydrocarbons entering chamber 53 by adding inert gases thereto, such as steam, nitrogen, hydrogen, etc. Forthis purpose hydrogen may be Withdrawn from line 25 by line 56, or I may omit fractionator 4| and conduct f rating wherein said C4 fraction contains a subthe dehydrogenated "butanes" and hydrogen directly from compressor 40 to isomerizer 53. When operating underthese conditions, hydrogen will accumulate in the gases at the top of fractionator 20 and may be removed therefrom by condensing or absorbing the hydrocarbons recycled through line 2l, in suitable apparatus not shown. Hydrogen separated in thisgway may be employed in heater 24 and hydrogenator 21, if desired.

In the operation of my process I prefer to polymerize in chamber I3 a hydrocarbon mixture containing at least as much isobutylene as 2- butene, as I have found that the motor fuel cb- -tained from the polymerization of an equi-mo- -lecular` mixture of these hydrocarbons has nearly as high a knock rating as the,motor fuel pre- 'pared by polymerization of pure isobutylene. By polymerizing the mixture, therefore, I find it possible to produce motor fuel of extremely high octane number without the expense of .converting all the raw material into isobutylene and purifying it. The exact composition of the copolymers is not known, but they are apparently highly branched octenes'andedo-decenes. I have found thatwhereas by polymerizing isobutylene alone with-phosphoric acid and silica I may obtain a fuel having an octane number of about .100, if an equi-molecular mixture of isobutylene and normal 2-butene is employed Iobtain a fuel (on reduction of the olefin to octanes) having an octanenumber of about 92-96. Polymerization of l-butene, on the other hand, produces, under substantially the same conditions, after hydrogenation, a fuel having an octane number of less 'than 60 and the polymerization of 2-butene alone Iyields a fuel with an octane number of only ,about 'I0-80. It will be observed, therefore, that polymerizing a mixture of butylenes is distinctly advantageous and it is desirable to employ enough isobutylene in the mixture to equal or exceed the amount of normal butylenes present in -order to obtain most satisfactory results. For

this purpose I may introduce additional amounts of isobutylene by line 51. This isobutylene may be obtained by carefulfractionation from butylene mixtures or by dehydration of isobutyl alcohol with alumina or thoria catalysts at about '750 F. It may also be obtained by yintroducing .isobutane into dehydrogenation chamber 31 by line 31a. Normal by line 31a and later the resulting normal butene may be isomerized in chamber 53. C4 hydrocarbons from natural gas, etc. which are substantially saturated may likewise` be introduced at 31a. Thusv I may employ somewhat lower or higher temperatures in polymerizer I3, for example 200 to 400 F. and in the isomerization step inl 53 I may conduct the operation at temperatures as high as 800 F. The' temperatures given are preferred with the catalysts described. Too low temperaturesmust-.be avoided in the isomerizer 53 to prevent excessive-polymerization of olens therein, but this difficulty may be largely overcome by reducing the time of contact and by diluting the gases with hydrogen, steam, etc.

Although I have described my invention with respect to certain embodiments thereof, it should be understood that it is not intended to limit it thereby, except insofar as set forth in the following claims.

I claim:

1. In the process of converting the unsaturated C4 fraction of a commercial hydrocarbon gas mixture into motor fuel octanes of high knock butane may also be introduced l stantial amount of isobutylene together with normal butenes land 2, the improvement comprising subjecting said C4 fraction topolymerization in the presence of an acid acting polymerizing catalyst at a temperature of about 250 to 350 whereby isobutylene is Asubstantially copolymerized with said. 2-butene into octene. separating the octene from the unconverted C4 hydrocarbons and subjecting said octene to hydrogenation to produce octanes, subjecting the unconverted C4 hydrocarbons to dehydrogenation in 'the presence ofa dehydrogenating catalyst at a temperature of about 850 to 1000 F., whereby butanes are substantially converted to butenes,

including Z-butene, and recycling said butenes thus obtained to said polymerization step with said C4 fraction first mentioned thereby increasing the amount of I 2-butene available and diminishing the amount of isobutylene polymer formation.

v 2. The process of claim 1 wherein said'C4 hydrocarbon fraction contains vabout 10 tov 15% of isobutylene and about 20 to 30%V of. normal butenes.

3. The process of claim l'wherein -the butenes obtained from the dehydrogenation stepare subjected to the action of an isomerizing catalyst at a temperature of about 400'to 480 F. and normal 1butene resulting from said dehydrogenation is substantially converted to 2-butene before recycling to said catalytic polymerization step,

thereby further increasing the amount of 2-butene available for cgi-polymerization with said isobutylene. I

4. In the process of claim 1 wherein'said C4 hydrocarbon fraction contains insufcient isobutylene to co-polymerize allI 2-butene present therein, the further improvement comprising subjecting butenes obtained from said dehydrogenation step to the action of an isomerizing catalyst at a temperature of about 480 to 800 F., whereby a substantial proportion of the normal butylenes contained in the dehydrogenation product are converted to isobutylene before recycling to said catalytic polymerization step.

tylene is produced from normal butylenes conf olefin mixture to polymerization in the presence of an acid acting polymerization catalyst whereby tained therein, and subsequently subjecting said I isobutylene and`2-butene are copolymerized; to

produce motor fuel octenes of high knock rating' and separating said octenes from unpolymerized C4 hydrocarbons.

6. The process of claim 5 wherein saidacid acting catalyst is phosphoric aciddisposed on a suitable solid supporting material.

'1.,l The process of claim 5 wherein the said motor fuel octenes are converted into otanes by subsequent hydrogenation.

8. The process of claim 5 wherein the concentration of isobutylene in said unsaturated C4 hydrocarbon fraction is adjusted by converting normal butylenes contained therein into isobutylene by the action of phosphoric acid at a temperature of 480-800" F.

9. The process of converting a commercial C4 hydrocarbon fraction into high knock rating motor fuels boiling within the gasoline range, which comprises dehydrogenating said C4 fraction by the action of a solid dehydrogenating catalyst thereby converting asubstantial proportion of said C4 hydrocarbons into butylenes, subjecting said butylenes to the action of an isomerizing catalyst `whereby normal butylenes are substantially converted into isobutyiene, subjecting said isomerized hydrocarbon mixture to the action'of a polymerizing catalyst at a temperature above 250 F. whereby said isobutylene is co-polymerized with 2-butene to produce high knock rating motor fuel, separating said high knock-rating motor fuel from unpolymerized hydrocarbon gases and recycling said gases to said catalytic dehydrogenation step iirst mentioned.

10. The process of claim 9 wherein the high knock rating motor fuel obtained from said copolymerization step is subsequently treated with hydrogen obtained from said dehydrogenation step in the presence of a suitable hydrogenating catalyst whereby said motor fuel is rendered substantially saturated.- A

11. The process of claim 9 wherein unconverted C4 hydrocarbons from said co-polymerizing step are recycled to said dehydrogenating step.

ROBERT F. MARSCHNER. 

